Unable To Apply Mysqld_db_t To Mysql Directory

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Hello,

A server was configured in /var/lib/myslq in the root fs. I added a LV
specifically for mysql. I stopped myql and renamed /var/lib/mysql to
/var/lib/mysql.old. I created a new dir /var/lib/mysql and mounted the LV
on /var/lib/mysql. I then copied with “cp -prZ” all mysql files in
/var/lib/mysql.old to /var/lib/mysql.

But then I got a selinux problem:
# ls -ldZ mysql.old/ mysql drwxr-xr-x. mysql mysql system_u:object_r:var_lib_t:s0 mysql drwxr-xr-x. mysql mysql system_u:object_r:mysqld_db_t:s0 mysql.old/

I tried to changed the context on mysql with the following commands:

# semanage fcontext -a -t mysqld_db_t “/var/lib/mysql(/.*)?”
# restorecon -R -v /var/lib/mysql

But the /var/lib/mysql directory didn’t take the change as you can see below:
# ls -ldZ mysql.old/ mysql drwxr-xr-x. mysql mysql system_u:object_r:var_lib_t:s0 mysql drwxr-xr-x. mysql mysql system_u:object_r:mysqld_db_t:s0 mysql.old/

How can I fix the wrong context on mysql directory?
Thanks,

6 thoughts on - Unable To Apply Mysqld_db_t To Mysql Directory

  • /var/lib/mysql is already in default policy – no need to add anything there

    can you please provide the output of ‘semanage fcontext -lC’ so that we can see any local selinux modifications made?

    From base policy with nothing added, for that directory, you *should*
    be able to just restorecon -Rv /var/lib/mysql and have the correct labelling.

  • Interesting to see the Equivalence. As a first thing, I tried:

    semanage fcontext -a -e /var/lib/mysql.old /var/lib/mysql then restorecon -R /var/lib/mysql

    # semanage fcontext -lC
    SELinux fcontext type Context

    /home/users(/.*)? all files system_u:object_r:user_home_dir_t:s0
    /var/lib/mysql all files system_u:object_r:mysqld_db_t:s0
    /var/lib/mysql(/.*)? all files system_u:object_r:mysqld_db_t:s0

    SELinux Local fcontext Equivalence

    ./mysql = ./mysql.old
    /var/lib/mysql = /var/lib/mysql.old mysql = ./mysql.old

  • Thanks, I managed to fix /var/lib/mysql

    # ls -ldZ /var/lib/mysql drwxr-xr-x. mysql mysql system_u:object_r:mysqld_db_t:s0 /var/lib/mysql

    To fix it, I tried:
    semanage fcontext -d -e /var/lib/mysql this command returned:
    KeyError: /var/lib/mysql I tried restorecon anyway:
    restorecon -Rv /var/lib/mysql But not better:
    ls -ldZ /var/lib/mysql drwxr-xr-x. mysql mysql system_u:object_r:var_lib_t:s0 /var/lib/mysql

    So I did the following:
    semanage fcontext -d -t var_lib_t /var/lib/mysql It started to look better:
    ls -ldZ /var/lib/mysql drwxr-xr-x. mysql mysql system_u:object_r:var_lib_t:s0 /var/lib/mysql Then I ran restorecon restorecon -Rv /var/lib/mysql I got a lot of :
    restorecon reset /var/lib/mysql/…

    And then I got the proper context on /var/lib/mysql.

    I think there are still many things I do not understand about SELinux.

    I thought the equivalence thing I did with the command below was going to assign the context of /var/lib/mysql.old to /var/lib/mysql. Obviously not!
    semanage fcontext -a -e /var/lib/mysql.old /var/lib/mysql

    I still have the following equivalence:
    # semanage fcontext -lC
    SELinux fcontext type Context

    /home/users(/.*)? all files system_u:object_r:user_home_dir_t:s0
    /var/lib/mysql all files system_u:object_r:mysqld_db_t:s0
    /var/lib/mysql(/.*)? all files system_u:object_r:mysqld_db_t:s0

    SELinux Local fcontext Equivalence

    ./mysql = ./mysql.old mysql = ./mysql.old

    Should I be worried about those two equivalence?

    Thanks, Bernard

  • I think you have a slight misconception over how labels are determined.

    There’s no relation between what is presently on the filesystem when you do ls -lZ and what the policy database thinks it ought to be.

    This is why you can chcon to change the label of something but a relabelling will change it back.

    When you run restorecon to relabel a path what happens is it takes the absolute (full) path and compares it against the regexes in the selinux policy database (see it with semanage fcontext -l for some, but now all, context matches) …

    Then for the most specific match it will apply whatever label is in that database.

    When you do semanage fcontext -a -e /foo /bar to do an alias what you are telling selinux is that for every time that /bar is run through the regex replace bar with foo and check that instead.

    This is why when adding custom labelling you need to do a full regex path to match files under that directory too.

    When you moved /var/lib/mysql to /var/lib/mysql.old the labels moved with the files (this is the default unless you cross filesystems, you can force labelling as the destination with mv -Z).

    The selinux database still has /var/lib/mysql(/.*)? as being type mysqldb_db_t even if that directory doesn’t exist.

    When the directory is created and put in place then it will get what policy says is right for that path.

    The point of using equivalence is when you move a default location –
    such as /home to /data/home or /var/lib/mysql to /data/mysql

    In that situation the default selinux policy doesn’t know anything about /data or the contents of it so it’ll end up with a default_t label … not very useful.

    Now you could semanage fcontext -a -t mysqldb_db_t /data/mysql(/.*)?
    but quite often the ‘story’ of a directory tree isn’t about just one label and it’d be tedious trying to match them all …

    For the craziness that is $HOME for instance…

    CentOS7: cat /etc/selinux/targeted/contexts/files/file_contexts.homedirs Fedora: cat /usr/share/selinux/targeted/default/active/homedir_template

    There’s a lot of different contexts depending on the file in that tree
    … trying to mimic them all to move /home to /data/home would be a nightmare …

    But this is made trivial with semanage fcontext -a -e /home /data/home to ensure ~/.ssh and ~/.gpg and ~/public_html and so on all get the right contexts.

    So based on that I hope you understand why the equivalence lines you have left are effectively meaningless – they are not absolute paths and so can’t match a tree to do the labelling replacement.

    Does that help make things a bit clearer on your file contexts?

    TL:DR; there was no need to “assign” as you were still using the default mysql DB path, just a restorecon would have solved it.

  • James,

    I read your email a couple of times. There is so much to learn from it.

    If I am right, the output of “semanage fcontext -l” is the content of the SELinux database regarding the SELinux contexts. Yet if I am right, when we try to assign or verify what should be the contexts on files or directories, a first look at the SELinux DB should be the first thing to do. Right?

    I have now a much better understanding of what is going on when I use
    “semanage fcontext -a -t …” then “restorecon -R”. “semanage fcontext -a”
    add fcontext the SELinux DB and restorecon applies the fcontext to the files or directory as defined in the DB.

    In the past I have been confused by chcon and came to the conclusion this command was totally useless. But if the command exist, it should have a use of it. What kind of situation could make chcon useful?

    Regarding the equivalence, at first I understood it as “make this equal to that”. A bit like when using chmod –reference. Wrong!!!

    I didn’t only have a slight misconception on label, I honestly would say I
    was lost with the new lights you made on it.

    Thanks a lot for your time James! I really appreciate it.

    Bernard

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